This is probably some weird thing on my system, but after updating RubyGems, I started getting errors like this when running Rake tasks
WARNING: Possible conflict with Rake extension: String#ext already exists WARNING: Possible conflict with Rake extension: String#pathmap already exists
I tried removing various gems, playing with versions and generally wasting a bit of time. In the end, a simple downgrade fixed me again:
gem update --system 1.7.2 bundle install
Hope this helps someone!